865

865 is a natural number that follows 864 and precedes 866. It is an odd composite number, with prime factorization 5 × 173, making it a semiprime. In various numeral systems it has the representations 1101100001 in binary, 0x361 in hexadecimal, and DCCCLXV in Roman numerals. The sum of its decimal digits is 19, which is a prime number.

In calendar terms, 865 CE sits in the 9th century. Traditional historical accounts describe Viking activity in the British Isles during this period, and the year is associated with the arrival of the Great Heathen Army in East Anglia, marking a significant phase in the incursions into Anglo-Saxon England.

In other uses, 865 is used as an area code in the North American Numbering Plan. Area code 865 serves a portion of East Tennessee, including the city of Knoxville and surrounding areas. The number may also appear in various cataloging, coding, or labeling systems where a numeric identifier is required.

Overall, 865 is primarily recognized as an integer with standard mathematical properties, a specific set of base representations, and incidental associations with historical events and regional telephone numbering.

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